Add stateless Streamable HTTP support (#392)
- It allows a single MCP session spanning multiple requests to be handled by different servers without sharing state - It does require the servers share data protection keys, but this is standard for ASP.NET Core cookies and antiforgery as well - It immediately throws for unsupported operations like sampling
This commit is contained in:
Stephen Halter
GitHub
parent
ca3a8ab921
commit
ce9f73f43f
10 changed files with 785 additions and 230 deletions
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@ -26,6 +26,7 @@ public static class HttpMcpServerBuilderExtensions
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builder.Services.TryAddSingleton<StreamableHttpHandler>();
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builder.Services.TryAddSingleton<SseHandler>();
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builder.Services.AddHostedService<IdleTrackingBackgroundService>();
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builder.Services.AddDataProtection();
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if (configureOptions is not null)
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{
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@ -1,10 +1,15 @@
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using ModelContextProtocol.Protocol.Transport;
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using ModelContextProtocol.AspNetCore.Stateless;
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using ModelContextProtocol.Protocol.Transport;
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using ModelContextProtocol.Server;
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using System.Security.Claims;
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namespace ModelContextProtocol.AspNetCore;
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internal sealed class HttpMcpSession<TTransport>(string sessionId, TTransport transport, ClaimsPrincipal user, TimeProvider timeProvider) : IAsyncDisposable
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internal sealed class HttpMcpSession<TTransport>(
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string sessionId,
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TTransport transport,
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UserIdClaim? userId,
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TimeProvider timeProvider) : IAsyncDisposable
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where TTransport : ITransport
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{
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private int _referenceCount;
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@ -13,7 +18,7 @@ internal sealed class HttpMcpSession<TTransport>(string sessionId, TTransport tr
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public string Id { get; } = sessionId;
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public TTransport Transport { get; } = transport;
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public (string Type, string Value, string Issuer)? UserIdClaim { get; } = GetUserIdClaim(user);
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public UserIdClaim? UserIdClaim { get; } = userId;
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public CancellationToken SessionClosed => _disposeCts.Token;
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@ -63,27 +68,7 @@ internal sealed class HttpMcpSession<TTransport>(string sessionId, TTransport tr
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}
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public bool HasSameUserId(ClaimsPrincipal user)
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=> UserIdClaim == GetUserIdClaim(user);
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// SignalR only checks for ClaimTypes.NameIdentifier in HttpConnectionDispatcher, but AspNetCore.Antiforgery checks that plus the sub and UPN claims.
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// However, we short-circuit unlike antiforgery since we expect to call this to verify MCP messages a lot more frequently than
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// verifying antiforgery tokens from <form> posts.
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private static (string Type, string Value, string Issuer)? GetUserIdClaim(ClaimsPrincipal user)
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{
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if (user?.Identity?.IsAuthenticated != true)
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{
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return null;
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}
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var claim = user.FindFirst(ClaimTypes.NameIdentifier) ?? user.FindFirst("sub") ?? user.FindFirst(ClaimTypes.Upn);
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if (claim is { } idClaim)
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{
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return (idClaim.Type, idClaim.Value, idClaim.Issuer);
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}
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return null;
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}
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=> UserIdClaim == StreamableHttpHandler.GetUserIdClaim(user);
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private sealed class UnreferenceDisposable(HttpMcpSession<TTransport> session, TimeProvider timeProvider) : IDisposable
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{
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@ -23,19 +23,37 @@ public class HttpServerTransportOptions
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public Func<HttpContext, IMcpServer, CancellationToken, Task>? RunSessionHandler { get; set; }
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/// <summary>
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/// Represents the duration of time the server will wait between any active requests before timing out an
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/// MCP session. This is checked in background every 5 seconds. A client trying to resume a session will
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/// receive a 404 status code and should restart their session. A client can keep their session open by
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/// keeping a GET request open. The default value is set to 2 hours.
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/// Gets or sets whether the server should run in a stateless mode that does not require all requests for a given session
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/// to arrive to the same ASP.NET Core application process.
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/// </summary>
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/// <remarks>
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/// If <see langword="true"/>, the "/sse" endpoint will be disabled, and client information will be round-tripped as part
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/// of the "mcp-session-id" header instead of stored in memory. Unsolicited server-to-client messages and all server-to-client
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/// requests are also unsupported, because any responses may arrive at another ASP.NET Core application process.
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/// Client sampling and roots capabilities are also disabled in stateless mode, because the server cannot make requests.
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/// Defaults to <see langword="false"/>.
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/// </remarks>
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public bool Stateless { get; set; }
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/// <summary>
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/// Gets or sets the duration of time the server will wait between any active requests before timing out an MCP session.
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/// </summary>
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/// <remarks>
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/// This is checked in background every 5 seconds. A client trying to resume a session will receive a 404 status code
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/// and should restart their session. A client can keep their session open by keeping a GET request open.
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/// Defaults to 2 hours.
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/// </remarks>
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public TimeSpan IdleTimeout { get; set; } = TimeSpan.FromHours(2);
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/// <summary>
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/// The maximum number of idle sessions to track. This is used to limit the number of sessions that can be idle at once.
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/// Gets or sets maximum number of idle sessions to track in memory. This is used to limit the number of sessions that can be idle at once.
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/// </summary>
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/// <remarks>
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/// Past this limit, the server will log a critical error and terminate the oldest idle sessions even if they have not reached
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/// their <see cref="IdleTimeout"/> until the idle session count is below this limit. Clients that keep their session open by
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/// keeping a GET request open will not count towards this limit. The default value is set to 100,000 sessions.
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/// </summary>
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/// keeping a GET request open will not count towards this limit.
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/// Defaults to 100,000 sessions.
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/// </remarks>
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public int MaxIdleSessionCount { get; set; } = 100_000;
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/// <summary>
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@ -12,7 +12,7 @@ internal sealed partial class IdleTrackingBackgroundService(
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ILogger<IdleTrackingBackgroundService> logger) : BackgroundService
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{
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// The compiler will complain about the parameter being unused otherwise despite the source generator.
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private ILogger _logger = logger;
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private readonly ILogger _logger = logger;
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protected override async Task ExecuteAsync(CancellationToken stoppingToken)
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{
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@ -35,20 +35,27 @@ public static class McpEndpointRouteBuilderExtensions
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.WithMetadata(new AcceptsMetadata(["application/json"]))
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, contentTypes: ["text/event-stream"]))
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status202Accepted));
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streamableHttpGroup.MapGet("", streamableHttpHandler.HandleGetRequestAsync)
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, contentTypes: ["text/event-stream"]));
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streamableHttpGroup.MapDelete("", streamableHttpHandler.HandleDeleteRequestAsync);
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// Map legacy HTTP with SSE endpoints.
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var sseHandler = endpoints.ServiceProvider.GetRequiredService<SseHandler>();
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var sseGroup = mcpGroup.MapGroup("")
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.WithDisplayName(b => $"MCP HTTP with SSE | {b.DisplayName}");
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if (!streamableHttpHandler.HttpServerTransportOptions.Stateless)
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{
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// The GET and DELETE endpoints are not mapped in Stateless mode since there's no way to send unsolicited messages
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// for the GET to handle, and there is no server-side state for the DELETE to clean up.
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streamableHttpGroup.MapGet("", streamableHttpHandler.HandleGetRequestAsync)
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, contentTypes: ["text/event-stream"]));
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streamableHttpGroup.MapDelete("", streamableHttpHandler.HandleDeleteRequestAsync);
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sseGroup.MapGet("/sse", sseHandler.HandleSseRequestAsync)
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, contentTypes: ["text/event-stream"]));
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sseGroup.MapPost("/message", sseHandler.HandleMessageRequestAsync)
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.WithMetadata(new AcceptsMetadata(["application/json"]))
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status202Accepted));
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// Map legacy HTTP with SSE endpoints only if not in Stateless mode, because we cannot guarantee the /message requests
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// will be handled by the same process as the /sse request.
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var sseHandler = endpoints.ServiceProvider.GetRequiredService<SseHandler>();
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var sseGroup = mcpGroup.MapGroup("")
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.WithDisplayName(b => $"MCP HTTP with SSE | {b.DisplayName}");
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sseGroup.MapGet("/sse", sseHandler.HandleSseRequestAsync)
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, contentTypes: ["text/event-stream"]));
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sseGroup.MapPost("/message", sseHandler.HandleMessageRequestAsync)
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.WithMetadata(new AcceptsMetadata(["application/json"]))
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.WithMetadata(new ProducesResponseTypeMetadata(StatusCodes.Status202Accepted));
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}
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return mcpGroup;
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}
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@ -34,7 +34,10 @@ internal sealed class SseHandler(
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var requestPath = (context.Request.PathBase + context.Request.Path).ToString();
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var endpointPattern = requestPath[..(requestPath.LastIndexOf('/') + 1)];
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await using var transport = new SseResponseStreamTransport(context.Response.Body, $"{endpointPattern}message?sessionId={sessionId}");
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await using var httpMcpSession = new HttpMcpSession<SseResponseStreamTransport>(sessionId, transport, context.User, httpMcpServerOptions.Value.TimeProvider);
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var userIdClaim = StreamableHttpHandler.GetUserIdClaim(context.User);
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await using var httpMcpSession = new HttpMcpSession<SseResponseStreamTransport>(sessionId, transport, userIdClaim, httpMcpServerOptions.Value.TimeProvider);
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if (!_sessions.TryAdd(sessionId, httpMcpSession))
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{
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throw new UnreachableException($"Unreachable given good entropy! Session with ID '{sessionId}' has already been created.");
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@ -0,0 +1,13 @@
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using ModelContextProtocol.Protocol.Types;
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using System.Text.Json.Serialization;
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namespace ModelContextProtocol.AspNetCore.Stateless;
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internal sealed class StatelessSessionId
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{
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[JsonPropertyName("clientInfo")]
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public Implementation? ClientInfo { get; init; }
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[JsonPropertyName("userIdClaim")]
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public UserIdClaim? UserIdClaim { get; init; }
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}
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@ -0,0 +1,6 @@
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using System.Text.Json.Serialization;
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namespace ModelContextProtocol.AspNetCore.Stateless;
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[JsonSerializable(typeof(StatelessSessionId))]
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internal sealed partial class StatelessSessionIdJsonContext : JsonSerializerContext;
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@ -0,0 +1,3 @@
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namespace ModelContextProtocol.AspNetCore.Stateless;
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internal sealed record UserIdClaim(string Type, string Value, string Issuer);
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@ -1,17 +1,22 @@
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using Microsoft.AspNetCore.Http;
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using Microsoft.AspNetCore.DataProtection;
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using Microsoft.AspNetCore.Http;
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using Microsoft.AspNetCore.Http.Features;
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using Microsoft.AspNetCore.WebUtilities;
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using Microsoft.Extensions.Logging;
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using Microsoft.Extensions.Options;
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using Microsoft.Net.Http.Headers;
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using ModelContextProtocol.AspNetCore.Stateless;
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using ModelContextProtocol.Protocol.Messages;
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using ModelContextProtocol.Protocol.Transport;
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using ModelContextProtocol.Protocol.Types;
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using ModelContextProtocol.Server;
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using ModelContextProtocol.Utils.Json;
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using System.Collections.Concurrent;
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using System.Diagnostics;
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using System.IO.Pipelines;
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using System.Security.Claims;
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using System.Security.Cryptography;
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using System.Text.Json;
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using System.Text.Json.Serialization.Metadata;
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namespace ModelContextProtocol.AspNetCore;
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@ -19,16 +24,22 @@ namespace ModelContextProtocol.AspNetCore;
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internal sealed class StreamableHttpHandler(
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IOptions<McpServerOptions> mcpServerOptionsSnapshot,
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IOptionsFactory<McpServerOptions> mcpServerOptionsFactory,
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IOptions<HttpServerTransportOptions> httpMcpServerOptions,
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IOptions<HttpServerTransportOptions> httpServerTransportOptions,
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IDataProtectionProvider dataProtection,
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ILoggerFactory loggerFactory,
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IServiceProvider applicationServices)
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{
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private static readonly JsonTypeInfo<JsonRpcError> s_errorTypeInfo = GetRequiredJsonTypeInfo<JsonRpcError>();
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private static readonly MediaTypeHeaderValue s_applicationJsonMediaType = new("application/json");
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private static readonly MediaTypeHeaderValue s_textEventStreamMediaType = new("text/event-stream");
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public ConcurrentDictionary<string, HttpMcpSession<StreamableHttpServerTransport>> Sessions { get; } = new(StringComparer.Ordinal);
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public HttpServerTransportOptions HttpServerTransportOptions => httpServerTransportOptions.Value;
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private IDataProtector Protector { get; } = dataProtection.CreateProtector("Microsoft.AspNetCore.StreamableHttpHandler.StatelessSessionId");
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public async Task HandlePostRequestAsync(HttpContext context)
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{
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// The Streamable HTTP spec mandates the client MUST accept both application/json and text/event-stream.
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@ -50,14 +61,28 @@ internal sealed class StreamableHttpHandler(
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return;
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}
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using var _ = session.AcquireReference();
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InitializeSseResponse(context);
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var wroteResponse = await session.Transport.HandlePostRequest(new HttpDuplexPipe(context), context.RequestAborted);
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if (!wroteResponse)
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try
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{
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// We wound up writing nothing, so there should be no Content-Type response header.
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context.Response.Headers.ContentType = (string?)null;
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context.Response.StatusCode = StatusCodes.Status202Accepted;
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using var _ = session.AcquireReference();
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InitializeSseResponse(context);
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var wroteResponse = await session.Transport.HandlePostRequest(new HttpDuplexPipe(context), context.RequestAborted);
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if (!wroteResponse)
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{
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// We wound up writing nothing, so there should be no Content-Type response header.
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context.Response.Headers.ContentType = (string?)null;
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context.Response.StatusCode = StatusCodes.Status202Accepted;
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}
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}
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finally
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{
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// Stateless sessions are 1:1 with HTTP requests and are outlived by the MCP session tracked by the mcp-session-id.
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// Non-stateless sessions are 1:1 with the mcp-session-id and outlive the POST request.
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// Non-stateless sessions get disposed by a DELETE request or the IdleTrackingBackgroundService.
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if (HttpServerTransportOptions.Stateless)
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{
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await session.DisposeAsync();
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}
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}
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}
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@ -108,27 +133,39 @@ internal sealed class StreamableHttpHandler(
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private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>?> GetSessionAsync(HttpContext context, string sessionId)
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{
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if (Sessions.TryGetValue(sessionId, out var existingSession))
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{
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if (!existingSession.HasSameUserId(context.User))
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{
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await WriteJsonRpcErrorAsync(context,
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"Forbidden: The currently authenticated user does not match the user who initiated the session.",
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StatusCodes.Status403Forbidden);
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return null;
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}
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HttpMcpSession<StreamableHttpServerTransport>? session;
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context.Response.Headers["mcp-session-id"] = existingSession.Id;
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context.Features.Set(existingSession.Server);
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return existingSession;
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if (HttpServerTransportOptions.Stateless)
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{
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var sessionJson = Protector.Unprotect(sessionId);
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var statelessSessionId = JsonSerializer.Deserialize(sessionJson, StatelessSessionIdJsonContext.Default.StatelessSessionId);
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var transport = new StreamableHttpServerTransport
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{
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Stateless = true,
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};
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session = await CreateSessionAsync(context, transport, sessionId, statelessSessionId);
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}
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else if (!Sessions.TryGetValue(sessionId, out session))
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{
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// -32001 isn't part of the MCP standard, but this is what the typescript-sdk currently does.
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// One of the few other usages I found was from some Ethereum JSON-RPC documentation and this
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// JSON-RPC library from Microsoft called StreamJsonRpc where it's called JsonRpcErrorCode.NoMarshaledObjectFound
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// https://learn.microsoft.com/dotnet/api/streamjsonrpc.protocol.jsonrpcerrorcode?view=streamjsonrpc-2.9#fields
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await WriteJsonRpcErrorAsync(context, "Session not found", StatusCodes.Status404NotFound, -32001);
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return null;
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}
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// -32001 isn't part of the MCP standard, but this is what the typescript-sdk currently does.
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// One of the few other usages I found was from some Ethereum JSON-RPC documentation and this
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// JSON-RPC library from Microsoft called StreamJsonRpc where it's called JsonRpcErrorCode.NoMarshaledObjectFound
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// https://learn.microsoft.com/dotnet/api/streamjsonrpc.protocol.jsonrpcerrorcode?view=streamjsonrpc-2.9#fields
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await WriteJsonRpcErrorAsync(context, "Session not found", StatusCodes.Status404NotFound, 32001);
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return null;
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if (!session.HasSameUserId(context.User))
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{
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await WriteJsonRpcErrorAsync(context,
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"Forbidden: The currently authenticated user does not match the user who initiated the session.",
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StatusCodes.Status403Forbidden);
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return null;
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}
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context.Response.Headers["mcp-session-id"] = session.Id;
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context.Features.Set(session.Server);
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return session;
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}
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private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>?> GetOrCreateSessionAsync(HttpContext context)
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@ -137,14 +174,7 @@ internal sealed class StreamableHttpHandler(
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if (string.IsNullOrEmpty(sessionId))
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{
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var session = await CreateSessionAsync(context);
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if (!Sessions.TryAdd(session.Id, session))
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{
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throw new UnreachableException($"Unreachable given good entropy! Session with ID '{sessionId}' has already been created.");
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}
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return session;
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return await StartNewSessionAsync(context);
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}
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else
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{
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@ -152,29 +182,79 @@ internal sealed class StreamableHttpHandler(
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}
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}
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private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>> CreateSessionAsync(HttpContext context)
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private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>> StartNewSessionAsync(HttpContext context)
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{
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var sessionId = MakeNewSessionId();
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context.Response.Headers["mcp-session-id"] = sessionId;
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string sessionId;
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StreamableHttpServerTransport transport;
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var mcpServerOptions = mcpServerOptionsSnapshot.Value;
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if (httpMcpServerOptions.Value.ConfigureSessionOptions is { } configureSessionOptions)
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if (!HttpServerTransportOptions.Stateless)
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{
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mcpServerOptions = mcpServerOptionsFactory.Create(Options.DefaultName);
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await configureSessionOptions(context, mcpServerOptions, context.RequestAborted);
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sessionId = MakeNewSessionId();
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transport = new();
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context.Response.Headers["mcp-session-id"] = sessionId;
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}
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else
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{
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// "(uninitialized stateless id)" is not written anywhere. We delay writing the mcp-session-id
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// until after we receive the initialize request with the client info we need to serialize.
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sessionId = "(uninitialized stateless id)";
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transport = new()
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{
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Stateless = true,
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};
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ScheduleStatelessSessionIdWrite(context, transport);
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}
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var transport = new StreamableHttpServerTransport();
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// Use application instead of request services, because the session will likely outlive the first initialization request.
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var server = McpServerFactory.Create(transport, mcpServerOptions, loggerFactory, applicationServices);
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var session = await CreateSessionAsync(context, transport, sessionId);
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// The HttpMcpSession is not stored between requests in stateless mode. Instead, the session is recreated from the mcp-session-id.
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if (!HttpServerTransportOptions.Stateless)
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{
|
||||
if (!Sessions.TryAdd(sessionId, session))
|
||||
{
|
||||
throw new UnreachableException($"Unreachable given good entropy! Session with ID '{sessionId}' has already been created.");
|
||||
}
|
||||
}
|
||||
|
||||
return session;
|
||||
}
|
||||
|
||||
private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>> CreateSessionAsync(
|
||||
HttpContext context,
|
||||
StreamableHttpServerTransport transport,
|
||||
string sessionId,
|
||||
StatelessSessionId? statelessId = null)
|
||||
{
|
||||
var mcpServerServices = applicationServices;
|
||||
var mcpServerOptions = mcpServerOptionsSnapshot.Value;
|
||||
if (statelessId is not null || HttpServerTransportOptions.ConfigureSessionOptions is not null)
|
||||
{
|
||||
mcpServerOptions = mcpServerOptionsFactory.Create(Options.DefaultName);
|
||||
|
||||
if (statelessId is not null)
|
||||
{
|
||||
// The session does not outlive the request in stateless mode.
|
||||
mcpServerServices = context.RequestServices;
|
||||
mcpServerOptions.ScopeRequests = false;
|
||||
mcpServerOptions.KnownClientInfo = statelessId.ClientInfo;
|
||||
}
|
||||
|
||||
if (HttpServerTransportOptions.ConfigureSessionOptions is { } configureSessionOptions)
|
||||
{
|
||||
await configureSessionOptions(context, mcpServerOptions, context.RequestAborted);
|
||||
}
|
||||
}
|
||||
|
||||
var server = McpServerFactory.Create(transport, mcpServerOptions, loggerFactory, mcpServerServices);
|
||||
context.Features.Set(server);
|
||||
|
||||
var session = new HttpMcpSession<StreamableHttpServerTransport>(sessionId, transport, context.User, httpMcpServerOptions.Value.TimeProvider)
|
||||
var userIdClaim = statelessId?.UserIdClaim ?? GetUserIdClaim(context.User);
|
||||
var session = new HttpMcpSession<StreamableHttpServerTransport>(sessionId, transport, userIdClaim, HttpServerTransportOptions.TimeProvider)
|
||||
{
|
||||
Server = server,
|
||||
};
|
||||
|
||||
var runSessionAsync = httpMcpServerOptions.Value.RunSessionHandler ?? RunSessionAsync;
|
||||
var runSessionAsync = HttpServerTransportOptions.RunSessionHandler ?? RunSessionAsync;
|
||||
session.ServerRunTask = runSessionAsync(context, server, session.SessionClosed);
|
||||
|
||||
return session;
|
||||
|
|
@ -210,9 +290,48 @@ internal sealed class StreamableHttpHandler(
|
|||
return WebEncoders.Base64UrlEncode(buffer);
|
||||
}
|
||||
|
||||
private void ScheduleStatelessSessionIdWrite(HttpContext context, StreamableHttpServerTransport transport)
|
||||
{
|
||||
context.Response.OnStarting(() =>
|
||||
{
|
||||
var statelessId = new StatelessSessionId
|
||||
{
|
||||
ClientInfo = transport?.InitializeRequest?.ClientInfo,
|
||||
UserIdClaim = GetUserIdClaim(context.User),
|
||||
};
|
||||
|
||||
var sessionJson = JsonSerializer.Serialize(statelessId, StatelessSessionIdJsonContext.Default.StatelessSessionId);
|
||||
var sessionId = Protector.Protect(sessionJson);
|
||||
|
||||
context.Response.Headers["mcp-session-id"] = sessionId;
|
||||
|
||||
return Task.CompletedTask;
|
||||
});
|
||||
}
|
||||
|
||||
internal static Task RunSessionAsync(HttpContext httpContext, IMcpServer session, CancellationToken requestAborted)
|
||||
=> session.RunAsync(requestAborted);
|
||||
|
||||
// SignalR only checks for ClaimTypes.NameIdentifier in HttpConnectionDispatcher, but AspNetCore.Antiforgery checks that plus the sub and UPN claims.
|
||||
// However, we short-circuit unlike antiforgery since we expect to call this to verify MCP messages a lot more frequently than
|
||||
// verifying antiforgery tokens from <form> posts.
|
||||
internal static UserIdClaim? GetUserIdClaim(ClaimsPrincipal user)
|
||||
{
|
||||
if (user?.Identity?.IsAuthenticated != true)
|
||||
{
|
||||
return null;
|
||||
}
|
||||
|
||||
var claim = user.FindFirst(ClaimTypes.NameIdentifier) ?? user.FindFirst("sub") ?? user.FindFirst(ClaimTypes.Upn);
|
||||
|
||||
if (claim is { } idClaim)
|
||||
{
|
||||
return new(idClaim.Type, idClaim.Value, idClaim.Issuer);
|
||||
}
|
||||
|
||||
return null;
|
||||
}
|
||||
|
||||
private static JsonTypeInfo<T> GetRequiredJsonTypeInfo<T>() => (JsonTypeInfo<T>)McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(T));
|
||||
|
||||
private sealed class HttpDuplexPipe(HttpContext context) : IDuplexPipe
|
||||
|
|
|
|||
Loading…
Reference in a new issue